Solid-state image pickup device with an improved output amplifier circuitry

1. A solid-state image pickup device comprising: a plurality of light sensing sections; a plurality of vertical transfer registers configured to transfer signal charge of the plurality of light sensing sections in the vertical direction; a horizontal transfer register configured to transfer the signal charge in the horizontal direction; a floating gate amplifier that is placed at an output side of the horizontal transfer register; a floating diffusion amplifier that is placed in a horizontal transfer register which is provided at a stage subsequent to the floating gate amplifier; and an overflow drain mechanism that is placed in the horizontal transfer register between the floating gate amplifier and the floating diffusion amplifier, wherein the floating gate amplifier has a conversion gain lower than that of the floating diffusion amplifier, wherein, in the solid-state image pickup device, verification is performed on an output signal from the floating gate amplifier and an output signal from the floating diffusion amplifier, wherein, in a case in which an original signal is provided within a limit of a dynamic range of the floating diffusion amplifier and is a small signal having a level that is lower than a level corresponding to an amount of signal charge remaining after draining is performed with the overflow drain mechanism, the output signal from the floating diffusion amplifier is employed, and wherein, in a case in which the original signal is a large signal having a level that is higher than the level corresponding to the amount of signal charge remaining, the output signal from the floating gate amplifier is employed.

2. The solid-state image pickup device according to claim 1 , wherein the horizontal transfer register that is placed in the vicinity of a floating diffusion unit which is included in the floating diffusion amplifier has a last transfer unit, a transfer channel width of the last transfer unit becoming smaller in a direction toward the floating diffusion unit.

3. The solid-state image pickup device according to claim 2 , wherein the overflow drain mechanism drains, from signal charge that has passed through the floating gate amplifier, excess charge in excess of an amount of charge that the floating diffusion amplifier or the last transfer unit is able to handle.

4. The solid-state image pickup device according to claim 3 , wherein a large amount of signal charge is read by the floating gate amplifier, and a small amount of signal charge is read by the floating diffusion amplifier.

5. The solid-state image pickup device according to claim 1 , wherein the overflow drain mechanism drains excess charge beyond a dynamic range of the floating diffusion amplifier.

6. The solid-state image pickup device according to claim 5 , wherein a large amount of signal charge is read by the floating gate amplifier, and a small amount of signal charge is read by the floating diffusion amplifier.

7. The solid-state image pickup device according to claim 5 , wherein the overflow drain mechanism includes an overflow control gate region and an overflow drain region.

8. The solid-state image pickup device according to claim 7 , wherein the overflow control gate region is configured to cause to be drained excess charge in excess of an amount of charge that the floating diffusion amplifier or a last transfer unit is able to handle.

9. The solid-state image pickup device according to claim 7 , wherein the overflow gate region is formed at a side portion of the horizontal transfer register.

10. A method for driving a solid-state image pickup device, the method comprising: reading, with a floating gate amplifier, a large amount of signal charge that has been transferred inside a horizontal transfer register; and reading, with a floating diffusion amplifier, a small amount of signal charge that has been transferred inside the horizontal transfer register, the floating diffusion amplifier being placed at a stage subsequent to the floating gate amplifier and having a conversion gain higher than that of the floating gate amplifier, wherein, from the large amount of signal charge that has passed through the floating gate amplifier, excess charge beyond a dynamic range of the floating diffusion amplifier is drained into an overflow drain mechanism, wherein verification is performed on an output signal from the floating gate amplifier and an output signal from the floating diffusion amplifier, wherein, in a case in which an original signal is provided within a limit of a dynamic range of the floating diffusion amplifier and is a small signal having a level that is lower than a level corresponding to an amount of signal charge remaining after draining is performed with the overflow drain mechanism, the output signal from the floating diffusion amplifier is employed, and wherein, in a case in which the original signal is a large signal having a level that is higher than the level corresponding to the amount of signal charge remaining, the output signal from the floating gate amplifier is employed.

11. The method for driving a solid-state image pickup device according to claim 10 , wherein, from the large amount of signal charge that has passed through the floating gate amplifier, excess charge in excess of an amount of charge that the floating diffusion amplifier or a last transfer unit is able to handle is drained into an overflow drain mechanism, a transfer channel width of the last transfer unit becoming smaller in a direction toward a floating diffusion unit.

12. An electronic apparatus comprising: an optical system; a solid-state image pickup device; and a signal processing circuit configured to process an output signal of the solid-state image pickup device, the solid-state image pickup device including a plurality of light sensing sections, a plurality of vertical transfer registers configured to transfer signal charge of the plurality of light sensing sections in the vertical direction, a horizontal transfer register configured to transfer the signal charge in the horizontal direction, a floating gate amplifier that is placed at an output side of the horizontal transfer register, a floating diffusion amplifier that is placed in a horizontal transfer register which is provided at a stage subsequent to the floating gate amplifier, and an overflow drain mechanism that is placed in the horizontal transfer register between the floating gate amplifier and the floating diffusion amplifier, wherein, in the solid-state image pickup device, the floating gate amplifier has a conversion gain lower than that of the floating diffusion amplifier, wherein in the solid-state image pickup device, verification is performed on an output signal from the floating gate amplifier and an output signal from the floating diffusion amplifier, wherein, in a case in which an original signal is provided within a limit of a dynamic range of the floating diffusion amplifier and is a small signal having a level that is lower than a level corresponding to an amount of signal charge remaining after draining is performed with the overflow drain mechanism, the output signal from the floating diffusion amplifier is employed, and wherein, in a case in which the original signal is a large signal having a level that is higher than the level corresponding to the amount of signal charge remaining, the output signal from the floating gate amplifier is employed.

13. The solid-state image pickup device according to claim 12 , wherein the overflow drain mechanism an overflow control gate region and an overflow drain region.

14. The solid-state image pickup device according to claim 13 , wherein the overflow control gate region is configured to cause to be drained excess charge in excess of an amount of charge that the floating diffusion amplifier or a last transfer unit is able to handle.

15. The solid-state image pickup device according to claim 13 , wherein the overflow gate region is formed at a side portion of the horizontal transfer register.